Question about washed yeast - airspace

For a sample of washed yeast in a canning jar, how important is it to have no air space? I got a sample from a friend with a few inches of airspace. I won't be brewing for a couple of weeks. Should I top it off with boiled, cooled water?

I don't think it matters as you will be decanting off as much of the water/beer as possible before pitching. If boiled water was used, there should be very little dissolved oxygen in it, assuming it was not shaken or disturbed.

I normally fill mine up with little head space but in your case I would just let it be. If it is ok up till now it should be fine for a few more weeks and opening it might introduce a infection.

I've only washed a couple times and I do try to fill them almost all the way to the top with no head space, but I do wonder how much it matters. I guess the thinking is the oxygen in the air above the liquid will go back into the water and somehow affect the yeast, right? Oxidation maybe? Anyone know why it's bad?

mtnagel said:

I've only washed a couple times and I do try to fill them almost all the way to the top with no head space, but I do wonder how much it matters. I guess the thinking is the oxygen in the air above the liquid will go back into the water and somehow affect the yeast, right? Oxidation maybe? Anyone know why it's bad?

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Oxygen is your enemy when storing yeast.

Ideally if you intend to store your liquid yeast for prolonged periods in a container in the fridge then rinse them to remove any foreign matter (hop residue,etc) and store under sterilized, de-oxygenated, distilled water with minimal headspace.
Dry yeast storage is also negatively affected by oxygen.

I am going to harvest some yeast from heady topper cans and want to store some of the yeasts after I make a starter for an extended period of time (2-3 months). Will it be ok if I store it in the fridge in a mason jar that I purged with co2 or should I really consider getting everything I need to freeze the yeast?

Should be fine. I've seen people say to use it within 6 months to a year. Personally I've only gone a few months, but just because I used it within then. You'll definitely want to take into account the reduced viability and make sure you make an appropriate starter before use, but it should be fine.

I've also heard that if you want to "reset the clock", you can make a smallish starter to basically wake it up, make it replicate some and then you can store that for a couple months if needed. I probably won't do that with my off the shelf yeast, but I plan to do that with my Conan because I don't know when I can get it again, so I'm hoping to keep it going for years that way. Someone will let me know if that's a bad idea.